The present invention relates to corrosion resistant weld overlay cladding alloys which can be used in high temperature, corrosive environments in order to prevent corrosion of stainless steels and particularly austenitic stainless steel equipment.
More particularly, the present invention is concerned with the prevention of corrosion in stainless steel components exposed to corrosive environments in chemical processing equipment and especially apparatus used in the manufacture of tall oils such as distillation towers. In carrying out such distillation, temperatures in the range of 400.degree. to 500.degree. F. are used and corrosive materials present in the tower include tall oil, oleic acid, sulfur compounds and traces of chlorides and other acidic and/or corrosive degradation materials. The original roll bond cladding is attached and in many cases had roughened surface giving the appearance of a sandpaper texture and in more advanced stages a uniform pitting. In some instances singular pits are located in the roll bond which actually penetrate the wall of the apparatus. It is theorized that these isolated pits are the result of imperfections in the roll bond clad and it is surmised that the pits might result from free iron imbedded in the clad during the building process. Thirdly, "washouts" in the alloy cladding occur in areas of the weld overlay. It is deemed that these washouts are caused by varying quality in the wire used in welding. A fourth defect is porosity of the weld in the alloy cladding which typically occurs between the weld beads. These corrosions effects necessitate frequent shutdown and repair of the apparatus which is not only costly but dangerous particularly in cases where the corrosion actually causes penetration through the apparatus wall.
Efforts to overcome such corrosion problem have included use of a variety of alloys, but these have not been successful. The result is either frequent shut-down and costly repair or, in some cases, extremely costly replacement of the corroded equipment.